The present invention relates to a rear projection screen for use in a projector, and more particularly, to a holographic screen for use in a rear projection screen.
A conventional rear projection screen contains a diffusion material. Rear projection screens commonly use a lenticular lens and a Fresnel lens. However, such a lenticular-Fresnel screen has a narrow angle of view and limited luminescence. As a result, a holographic screen has been proposed to overcome these problems.
Since holographic screens are manufactured easily once a master is fabricated and the features of the screen can be adjusted easily, holographic screens are popular in rear projection screens.
FIG. 1A is a perspective view showing a conventional holographic screen which is used as a rear projection screen. FIG. 1B is a sectional view cut along line 1--1 of the screen of FIG. 1A. The holographic screen, having a variety of shapes, comprises a Fresnel lens sheet 6 and a holographic sheet 8. The holographic screen is made of a polymer of a transparent acryl-group such as acryl and polymethylmetacrylate (PMMA). The Fresnel lens sheet 6 is located between a projection light source and the holographic sheet 8, and has an uneven shape on the surface opposite the light source, which varies a focal point of projection light incident from a light source, on the surface opposite the light source. Thus, the projection light transmitting the Fresnel lens sheet 6 has a substantially uniform light distribution on the surface of the holographic screen. The projection light output from the Fresnel lens sheet 6 is incident to the holographic sheet 8. The holographic sheet 8 is formed on the viewing surface of the holographic screen, and has a diffusion plate function for forming an image by scattering the light incident from the Fresnel lens sheet 6. Protrusions 4 constituting the holographic sheet 8 are formed on the viewing surface of the screen and are disposed in parallel with the vertical axis of the holographic sheet 8. The protrusions 4 are spaced from each other in predetermined intervals along the horizontal direction of the screen. Most of the light incident from the Fresnel lens sheet 6 projects onto the holographic sheet 8. The projection light incident to the holographic sheet 8 is scattered by the protrusions 4 to form an image.
However, due to low contrast, an image formed on the holographic screen is not completely discernable in ambient light.